add simple method to get the certificate leaf.
add simple method to get the certificate leaf.

AaronFriel/hs-tls,tolysz/hs-tls,beni55/hs-tls,erikd/hs-tls,lancelotsix/hs-tls,beni55/hs-tls,lancelotsix/hs-tls,tolysz/hs-tls,AaronFriel/hs-tls,erikd/hs-tls